The evaluation of retinal structure as determined by photographic documentation of the three month follow-up examination has indicated a favorable outcome in eyes treated in the CRYO-ROP trial. Additional follow-up of these infants is essential in order to evaluate the long-term safety and efficacy of trans-scleral cryotherapy, to determine the optimal disease threshold for treatment and to define the indications for routine follow-up in infants with mild retinopathy of prematurity. The primary outcome measure of the CRYO-ROP study was retinal integrity as determined by photographic documentation one year after cryotherapy. Since this study began in 1986, the technology for measuring visual function in infants has evolved to the point where it has been possible to add a second outcome measure one year after treatment. This is grating visual acuity, as assessed monocularly by the Teller Acuity Card method. We propose to continue evaluating retinal structure and visual function in infants in the CRYO-ROP trial for an additional five-year follow-up period. These data will correlate for the first time structural changes observed in both acute proliferative and scarring phases of retinopathy of prematurity (ROP) with the eventual visual function of the eye. We will also evaluate the long-term risk/benefit ratio of cryotherapy in infants with differing degrees of ROP and document the long-term ocular status and visual outcome of very low birth weight infants with varying degrees of treated or untreated ROP. Three specific questions will be examined: 1. Are there long-term structural or functional ocular sequelae in eyes treated with cryotherapy that would require re-evaluation of the risk/benefit ratio of recommending cryotherapy? 2. Do long-term data on structural and functional sequelae in untreated eyes with ROP indicate that the "threshold" for cryotherapy should be lowered? 3. Is the incidence of structural or functional ocular abnormalities any different in infants with mild ROP than in infants with no ROP? If not, future resources could be focused on follow-up of infants who have moderate or severe ROP.